Keratinous surfaces (e.g. skin and hair) are typically cleaned using surfactant-based compositions to remove dirt, soils and excess sebum. However, the cleansing process has disadvantages in that it removes essential/advantageous components from the keratinous surfaces during cleansing. This can lead to an unpleasant feel, e.g., hair can be draggy, entangled and unmanageable, and have a loss of softness and shine, and/or skin or scalp can feel dry, tight and/or itchy and in some cases show redness. Further, it is desirable to provide benefits from cleansing compositions beyond foaming and removal of dirt, soils and excess sebum. A variety of approaches have been developed to alleviate the disadvantages from the cleansing process and to enhance additional benefits beyond foaming and cleansing. For example, cleansing compositions can comprise (in addition to surfactants) oils like silicone oils, vegetable oils and mineral oils to provide e.g. a soft feel and enhanced moisturization to the cleaned surfaces. It is also very common to incorporate cationic components (in most cases cationic polymers) into cleansing compositions to provide enhanced sensorial attributes to the cleaned surfaces, e.g. softness, or improved functional qualities, e.g. detangling and anti-static benefits. These types of additives in cleansing compositions are usually referred to as conditioning agents. Cleansing compositions can also contain additional benefit agents such as zinc pyrithione, salicylic acid or hyaluronic acid. In order for these conditioning agents and the benefit agents to perform, they have to be deposited during the cleansing process onto the surface (e.g. skin and hair).
A common challenge encountered in cleansing compositions is efficacy of deposition of conditioning agents and benefit agents onto the cleaned surfaces. Typically, only a fraction of the agents is deposited and the rest is washed/rinsed off. Keratinous surfaces characteristically have some anionic surface charge; consequently cationic components can adhere to a certain degree onto the keratinous surfaces via electrostatic interaction. Therefore, cationic components, cationic polymers in particular, are used in cleansing compositions as conditioning agents. Through a process typically referred to as “coacervation” or “complexation” or “dilution precipitation”, cationic polymers can improve deposition efficacy of conditioning agents such as emollients, oils, other benefit agents and the cationic polymers themselves. In this process, the cationic polymer forms insoluble complexes with anionic surfactant during use of the cleansing composition, i.e. upon dilution. These insoluble complexes or coacervates can enhance deposition efficacy of the cationic polymers as well as water-insoluble components such as oils.
The concept of combining anionic surfactant and cationic polymer is used in many cleansing compositions today. Coacervate formation is dependent upon a variety of criteria such as molecular weight, charge density, pH, and temperature. Coacervate systems and the effect of these parameters have previously been studied and disclosed in, for example, J. Caelles, et al., Cosmetics & Toiletries, Vol. 106, April 1991, pp 49-54, C. J. van Oss, J. Dispersion Science and Technology, Vol. 9 (5,6), 1988-89, pp 561-573, D. J. Burgess, J. of Colloid and Interface Science, Vol. 140, No. 1, November 1990, pp 227-238, S. Zhou et al., Langmuir, 20, 2004, 8482-8489, and C. Lepilleur et al., J. Cosmet. Sci., 62, March/April 2011, 161-177. Consequently, approaches to improve the deposition from cleansing compositions include optimization of the cationic polymer as well as of the surfactant system. Optimization of the cationic polymer includes variation of cationic charge density, molecular weight, backbone chemistry and chemistry of the cationic moiety. The surfactant system in the cleansing composition is typically adjusted to the specific cationic polymer utilized to enhance efficiency, compatibility and formulation stability (or vice versa). Several examples of these approaches are disclosed in U.S Pat. Application No. 2003/0108507 and references therein.
However, this reference also discloses a deposition efficacy of only 2-3% (200-300 ppm/% active level in formulation) for small dispersed actives (that is, benefit agent materials that are insoluble in the cleansing formulation and exist as particles or droplets suspended in the cleansing formulation) having a size of less than or equal to 2 μm. A deposition efficacy of only 2-3% shows the general need for improving deposition efficacy from cleanser formulations. Further, the utilization of complexation of anionic surfactants and cationic polymer leads to the deposition of certain amounts of anionic surfactant, present in the coacervate, onto the keratinous surface. This surfactant deposition is undesirable, as anionic surfactants can exhibit high irritation potential when left on skin, and anionic surfactants can denature the keratin components of skin and hair, leading to undesirable morphological changes in these substrates.
Additionally, compositions utilizing complexation of anionic surfactant and cationic polymer typically do not provide any enhancement/aid of depositing water-soluble benefit agents because such benefit agents are not efficiently captured in the polymer-surfactant coacervates upon dilution and thus, are not deposited.
Another approach to enhance deposition efficacy of certain benefit agents described in the prior art is introducing cationic charges to the benefit agents such as emollients, humectants, and waxes. The cationic charges can facilitate adhesion of benefit agents onto surfaces with anionic surface charges such as hair and skin. However, such an approach requires chemical modification of the benefit agent with additional cationic moieties or encapsulation of the benefit agent with cationic materials—both of which may or may not be feasible.
It is reported in the prior art that presence of anionic polymer in compositions with cationic polymer and anionic surfactant does not lead to any improvement of deposition efficacy. For example, anionic rheology modifier polymers like Carbomer and Acrylates Copolymer have been shown to have detrimental effects on deposition efficacy, as e.g. disclosed in WO 2014/137859 A1. Specifically, this reference states that the presence of typical rheology polymers such as anionic acrylic copolymers (e.g. Carbopols) does not improve deposition efficacy of silicone oils. Further, they even severely reduce the deposition efficacy of silicone oils when the silicone oils are of smaller particle size (e.g. average oil droplet size of less than 5 micrometers). This reference further states that the “silicone deposition is inversely proportional to the amount of the acrylic stabilizer thickener present”. The reference discloses the use of a nonionic amphiphilic rheology modifying polymer to stabilize the composition “without interfering with the deposition of the silicone material” and is silent on how to improve deposition efficacy.
In summary, despite the various approaches used in the prior art to improve conditioning and deposition efficacy from cleansing formulations, there still remain disadvantages to the prior art, such as: low deposition efficacy, potential irritation from deposition of surfactant, limited compatibility with anionic polymers, and lack of aid in deposition of water-soluble components other than surfactants. As such, it remains desirable to provide improved cleansing compositions with optimum performance and enhanced deposition efficacy.